techause

iTrader: (11)

If the map sensor is measuring absolute pressure in the intake manifold(both vaccum...low pressure and high pressure values....which relates to engine load) and the boost gauge is plummed into a line which reads vaccum and boost(high pressure) connected to the intake manifold, are their values similar? In other words is boost another, less accurate/sensitive way to measure engine load?

-j

This may sound like a noob question, but I am really trying to get a good handle on EFI tuning and engine managment.

MalibuJack

iTrader: (5)

Vacuum/boost gauges have always been used in the past to show some level of engine running condition, back in the 60's and 70's vacuum gauges were used as an indicator of fuel economy.

In our cars the MAP sensor located in the MAF sensor and I think its only used to read atmospheric pressure (and the slight fluctuations caused by airflow through the sensor)

Boost/Vacuum gauges cannot accurately indicate true engine load however, since there's several factors that can contribute to those readings, throttle position, boost, dv, wastegate, leaks, etc.. Although airflow is a measure of how much demand there is on the engine, it doesnt reflect true load since those other variables have an effect.

techause

iTrader: (11)

Thanks for the quick reply. The readings are of similar value(both pressure in the manifold), however they are, by no means, interchangeable. I am not using a MAF, rather a 3.5 bar MAP, ported into the intake manifold...that is why I asked the question....I know, I ask too many questions

Thx again.

-J

MalibuJack

iTrader: (5)

Nah, I understand where your coming from.. however MAP reading, TPS, RPM, and IAT are the reference signals used in speed density.. all of which are needed to determine the fuel requirement on the engine, hence a good indicator engine load..

Ted B

iTrader: (6)

AFAIK, yes. A MAP/DIFF (MAP that measures boost as well as vacuum) will see the same readings as your boost gauge. Since a speed density system has no means of actually measuring airflow, it depends on pressure readings (MAP) that correlate to a programmed fuel map. It uses this data to make assumptions with regard to fuel requirement.